[VPlan] Use unique_ptr to clean up duplicated plan.

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -10141,9 +10141,10 @@ bool LoopVectorizePass::processLoop(Loop *L) {
         EpilogueVectorizerMainLoop MainILV(L, PSE, LI, DT, TLI, TTI, AC, ORE,
                                            EPI, &LVL, &CM, BFI, PSI, Checks);
 
-        VPlan &BestMainPlan = *LVP.getBestPlanFor(EPI.MainLoopVF).duplicate();
+        std::unique_ptr<VPlan> BestMainPlan(
+            LVP.getBestPlanFor(EPI.MainLoopVF).duplicate());
         const auto &[ExpandedSCEVs, ReductionResumeValues] = LVP.executePlan(
-            EPI.MainLoopVF, EPI.MainLoopUF, BestMainPlan, MainILV, DT, true);
+            EPI.MainLoopVF, EPI.MainLoopUF, *BestMainPlan, MainILV, DT, true);
         ++LoopsVectorized;
 
         // Second pass vectorizes the epilogue and adjusts the control flow